DKDP Research Articles

Effect of supersaturation on deuteration distribution in K(H1‐xDx)2PO4 crystals

The homogeneity of deuterium distribution in potassium dideuterium phosphate single crystals was studied by Raman and infrared spectroscopy analyses. Results indicated that the pyramidal section exhibited more homogeneous deuterium distribution than the prismatic section. Supersaturation slightly affected the deuterium homogeneity in the pyramidal section of crystals grown rapidly from 80% deuterated solution. Deuterium homogeneity in the prismatic section decreased with increasing supersaturation level of the growth solution.

Thermal effects in the DKDP Pockels cells in the 215–300 K temperature range

The thermal and electro-optical effects in Pockels cells with deuterated potassium dihydrogen phosphate (DKDP) crystals in the 215-300 K temperature range were investigated. Half-wave voltage decreases linearly with cooling, thereby it reduces seven times (up to 1 kW) with cooling to 215 K. The optical power of the thermally induced lens falls twice on cooling to 215 K from 300 K; thermally induced depolarization is almost independent of temperature and determined by input radiation power. A significant reduction of the thermally induced depolarization in a DKDP crystal with the axis inclined to the polarization plane of the beam was demonstrated numerically and experimentally. Thus, the DKDP crystals cooled to 215 K allow the creation of a low-voltage Pockels cell working with a high average and peak laser power.

New Water Vapor Barrier Film Based on Lamellar Aliphatic-Monoamine-Bridged Polysilsesquioxane.

Siloxane-based hybrid lamellar materials with ordered nanostructure units paralleling to the substrate have been widely used for water vapor barrier. However, it is very difficult to control the orientation of the lamellar units at molecular level. In this Research Article, a new lamellar bridged polysilsesquioxane (BPSQ) film, whose voids between lamellae were filled by pendant alkyl chains in the organic bridge, was prepared via the stoichiometric reaction between 3-glycidoxypropyltrimethoxysilane and aliphatic monoamine at 60 °C without catalyst. Experimental evidence obtained from FT-IR, MS, NMR, and GIXRD techniques suggested that the as-prepared BPSQ films were constructed by lamellar units with disordered orientation. Nonetheless, they possessed satisfactory water vapor barrier performance for potassium dihydrogen phosphate (KDP) and deuterated potassium dihydrogen phosphate (DKDP) optical crystals, and the water vapor transmission rate through BPSQ film with thickness of 25 μm was as low as 20.3 g·m(-2)·d(-1). Those results proved that filling the voids between molecular lamellae with alkyl chains greatly weakened the effect of lamellar unit orientation on the vapor barrier property of BPSQ film.

High power single-frequency and frequency-doubled laser with active compensation for the thermal lens effect of terbium gallium garnet crystal.

The thermal lens effect of terbium gallium garnet (TGG) crystal in a high power single-frequency laser severely limits the output power and the beam quality of the laser. By inserting a potassium dideuterium phosphate (DKDP) slice with negative thermo-optical coefficient into the laser resonator, the harmful influence of the thermal lens effect of the TGG crystal can be effectively mitigated. Using this method, the stable range of the laser is broadened, the bistability phenomenon of the laser during the process of changing the pump power is completely eliminated, the highest output power of an all-solid-state continuous-wave intracavity-frequency-doubling single-frequency laser at 532 nm is enhanced to 30.2 W, and the beam quality of the laser is significantly improved.

Habit control of deuterated potassium dihydrogen phosphate crystal for laser applications

In this study we investigate the habit of partially deuterated potassium dihydrogen phosphate (DKDP) crystals in the presence of Al3+ ions. We have grown single DKDP crystals in (50wt% and 80wt%) partially deuterated solutions and in solutions doped with Al3+ ions (2 ppm) by the point-seed rapid growth technique at controlled supercooling (ΔT=10°C). The growth length of each crystal face was measured and the aspect ratio was calculated. We found that crystals grown in partially deuterated solutions are similar in aspect ratio, while, crystals grown in deuterated solutions doped with Al3+ ions showed a relative change in aspect ratio, the crystal increased in size in the pyramidal direction (vertical axis direction). Crystal characteristics were also analyzed by X-ray diffraction, FTIR and Raman spectroscopy. We have speculated that the relative habit modification is due to a probably adsorption and inclusions of Al3+ ions in the prismatic section of the crystal.

Glass transition in ferroic glass Kx(ND4)1−xD2PO4: a complete x-ray diffraction line shape analysis

Quenching of dynamic disorder in glassy systems is termed as the glass transition. Ferroic glasses belong to the class of paracrystalline materials having crystallographic order in-between that of a perfect crystal and amorphous material, a classic example of ferroic glass is the solid solution of ferroelectric deuterated potassium dihydrogen phosphate and antiferroelectric deuterated ammonium dihydrogen phosphate. Lowering temperature of this ferroic glass can lead to a glass transition to a quenched disordered state. The subtle atomic rearrangement that takes place at such a glass transition can be revealed by careful examination of the temperature induced changes occurring in the x-ray powder diffraction (XRD) patterns of these materials. Hence we report here results of a complete diffraction line shape analysis of the XRD patterns recorded at different temperatures from deuterated mixed crystals DKxA1−xDP with mixing concentration x ranging as 0 < x < 1. Changes observed in diffraction peak shapes have been explained on the basis of structural rearrangements induced by changing O–D–O hydrogen bond dynamics in these paracrystals.

Measurement of Raman scattering gain coefficient in large-aperture DKDP crystals irradiated by 351 nm pulses

Transverse stimulated Raman scattering (TSRS) gain coefficient in a large aperture 65% deuterated potassium dihydrogen phosphate (DKDP) is measured at 351 nm. The measurement involves the use of an optical fiber sensor system to detect Raman scattering light in the DKDP crystal. A Raman scattering gain coefficient of 0.109 cm/GW is obtained and will be used to set upper limit of the DKDP crystals in our laser facility to avoid the TSRS induced energy loss and laser damage. The effect of bulk damage on growth behavior of TSRS is also examined and it is found that bulk damage has little impact on the TSRS growth. Thus the influence of bulk damage on the measurement of TSRS gain coefficient can be ignored.

Characteristics of Laser-Induced Surface and Bulk Damage of Large-Aperture Deuterated Potassium Dihydrogen Phosphate at 351 nm**Supported by the National Natural Science Foundation of China under Grant No 61505187.

Deuterated potassium dihydrogen phosphate damage performance at 351 nm is studied on a large-aperture laser system. Bulk and rear-surface damage are initiated under the 3ω fluences of 6.7 J/cm2 and 3 J/cm2, and show different growth characteristics under multiple laser irradiations with the fluence of 6 J/cm2. The size and number of bulk damage keep unchanged once initiated. However, surface damage size also does not grow, while surface damage number increases linearly with laser shots. Different damage thresholds and growth behaviors suggest different formations of bulk and surface damage precursors. The cause of surface damage is supposed to be near-surface absorbing particles buried under the sol-gel coating.

Study of the degree of deuteration on the microhardness of deuterated potassium dihydrogen phosphate crystals

A series of deuterated potassium dihydrogen phosphate (DKDP) crystals with different degrees of deuteration are grown from aqueous solution by the point-seed technique. The microhardness of (100), (001) and so-called ‘tripler’ faces for these DKDP crystals were measured. Initially the hardness number of (001) face for each crystal increases with the increase of the applied load until it reaches 25 g. With further increase in load, the hardness number decreases gradually. The hardness numbers decline with the increase in deuterium content. These composition dependences are expected since the bond strength is weakened by the substitution of deuterium for hydrogen. The hydrogen bond is considered to play the key role in effecting the crystal’s hardness. The visible hardness anisotropy of the different faces is attributed to the inhomogeneous distribution of the oxygen–hydrogen bond on these faces.

Partially deuterated potassium dihydrogen phosphate optimized for ultra-broadband optical parametric amplification

The refractive index of a potassium dihydrogen phosphate (KDP) crystal strongly depends on the deuteration fraction of the crystal. The wavelength dependence of the phase-matching angle in the near-infrared optical parametric process shows convex and concave characteristics for pure KDP and pure deuterated KDP (DKDP), respectively, when pumped by the second harmonic of Nd- or Yb-doped solid state lasers. Using these characteristics, ultra-broadband phase matching can be realized by optimization of the deuteration fraction. The refractive index of DKDP that was grown with a different deuteration fraction (known as partially deuterated KDP or pDKDP) was measured over a wide wavelength range of 0.4–1.5 μm by the minimum deviation method. The wavelength dispersions of the measured refractive indices were fitted using a modified Sellmeier equation, and the deuteration fraction dependence was analyzed using the Lorentz–Lorenz equation. The wavelength-dependent phase-matching angle for an arbitrary deuteration fraction was then calculated for optical parametric amplification with pumping at a wavelength of 526.5 nm. The results revealed that a refractive index database with precision of more than 2 × 10−5 was necessary for exact evaluation of the phase-matching condition. An ultra-broad gain bandwidth of up to 490 nm will be feasible when using the 68% pDKDP crystal.

Study of the charge-accumulation and -relaxation kinetics in a solid dielectric when it is electron-irradiated by an optical method

This paper discusses the kinetics of the accumulation and relaxation of electric charge in layers of the dielectric MgO+Al2O3 when it is irradiated with electrons having energy 1.6 keV. An optical method is used for the first time, based on the phase modulation of light caused by the electric field of the charge in an electrooptic crystal of deuterated potassium dihydrogen phosphate. It is established that the charge accumulated in the dielectric varies with time according to a linear law when the current density in the beam is 0.28×10−4–1×10−4 A/cm2, which corresponds to the electron flux density 1.7×1014–6×1014 cm−2. The charge relaxation is significantly accelerated if the charged dielectric is irradiated by an electron beam, creating particles in it with the opposite charge. The positive charge in this case relaxes at a greater rate than does the negative charge. This is apparently because electrons have higher mobility than do holes.

Principle of ultra precision polishing with micro water mist for KDP/DKDP crystals

Potassium dihydrogen phosphate (KDP) or deuterated potassium dihydrogen phosphate (DKDP) crystals are difficult to machine because they are soft and hygroscopic. Based on the deliquescence nature of KDP/DKDP crystals, a novel polishing method with micro water mist for KDP/DKDP crystals was proposed in this paper. The processing principle was investigated and polishing experiments with this method were carried out. The results show that the crystals can be machined by this method and the maximum material removal rate can reach 2.02 µm/min. A polished surface with root-mean-square roughness 47.6 nm was achieved by polishing with micro water mist in 10 min. The material removing principle and the planarisation mechanism were experimentally explained and verified.

Phase matching characteristics of deuterated ammonium dihydrogen phosphate crystals

Refractive indices for crystals ammonium dihydrogen phosphate (ADP), 30% deuterated ADP (DADP), 50% DADP, and 70% DADP are measured from 253 to 1529 nm with 5 × 10-6 accuracy. Numerical fits to modified double-pole Sellmeier equation are made. Second-harmonic generation, third-harmonic generation phase matching (PM) angles, and noncritical PM (NCPM) wavelengths are calculated using the Sellmeier parameters. The deuterated crystals show smaller PM angles than pure crystal. Fourth-harmonic generation process can be realized by DADP in smaller deuterium content than deuterated potassium dihydrogen phosphate (DKDP). The measured NCPM wavelengths are consistent with the calculated value. PM characteristics are compared between DADP and DKDP.

Rapid growth of a large size, highly deuterated DKDP crystal and its efficient noncritical phase matching fourth-harmonic-generation of a Nd:YAG laser

Large size DKDP crystal with high and homogenous deuterium content contributes to efficient noncritical phase matching FHG of ND:YAG laser.

Influence of deuteration on the KH2PO4 crystal micro-defects characterization by using positron annihilation spectroscopy

Deuterated potassium dihydrogen phosphate (K(DxH1-x) 2PO4) crystals with different deuteration levels (x=0, 0.51, 0.85) were grown by conventional cooling method from deuterated solutions at Shandong University. Positron annihilation spectroscopy has been widely used to the study on micro-defects of semiconductors and other materials, which is very sensitive to the crystal structure, defect types, defect concentrations, and so on. In this paper, positron annihilation spectroscopies (positron annihilation lifetime spectroscopy and Doppler broadening spectroscopy), combined with X-ray diffraction (XRD) are used to investigate micro-defects characterization in K(DxH1-x) 2PO4 crystals. Influences of deuteration degree on the crystal structure characteristics, defect types and concentrations are discussed. It can be concluded from XRD experiments that the lattice parameters of a and b increase with the increase in deuteration levels, while no obvious change occurs on the lattice parameter c. KH2PO4(KDP) crystals at low deuteration level and high deuteration level could be regarded as low deuterium-doped KDP crystal and low hydrogen-doped DKDP crystal respectively. It is indicated that the higher the replacement ratio in the crystals, the weaker the diffraction peak they show. Positron annihilation lifetimes increase clearly in the highly-deuterated KDP crystals. It is found that neutral interstitial defects and oxygen defects in the KDP crystal increase with increasing deuteration degree. And these types of defects can be attributed to lattice distortion effect. From positron annihilation lifetime results we can arrive at another conclusion that the compound defects will form and defects concentration is declined, when hydrogen vacancies, K vacancies and substitutional impurity defects continue to react by means of association reactions. These phenomena suggest that high deuteration plays a significant role in promoting association reaction of internal defects in the crystals. Furthermore, the polymerization reaction of the clusters and micro-cavities continue to occur, therefore defect concentrations will show a constant decrease. Doppler broadening spectra show that the internal defects in the crystals increase integrally with an increase of deuteration level; this agrees well with the results of positron annihilation lifetime. Moreover, Doppler broadening spectra indicate that the proportional change of these defects is synchronous and consistent with the actuality. To sum up, our experimental results suggest that the defect reaction is weak in low degree of KDP crystal deuteration growth (less than 50%), while reaction is enhanced in the high degree of deuteration growth (higher than 50%).

Bandwidth analysis of type-I optical parametric chirped pulse amplification systems

We propose a set of empirical formulas to describe the signal broadband gain regime and ultra-broadband gain point under a given pump wavelength for a type-I optical parametric chirped pulse amplification (OPCPA) system. These formulas are applied in the usual nonlinear crystals (beta barium borate, potassium dihydrogen phosphate, deuterated potassium dihydrogen phosphate, cesium lithium borate, lithium triborate, and yttrium calcium oxoborate), and the corresponding results agree with numerically calculated ones. The empirical formulas provide guidelines for selecting appropriate crystals or pump wavelengths to design OPCPA for broadband or ultra-broadband gain bandwidths with appointed signal wavelength.

Analysis of nonlinear optical propagation in a longitudinal deuterated potassium dihydrogen phosphate Pockels cell

Nonlinear optical propagation in a longitudinal deuterated potassium dihydrogen phosphate (DKDP) Pockels cell (PC) is studied analytically and with numerical simulations. Propagation equations are developed taking into account the nonlinear susceptibility tensor and the modification of the polarization state because of the voltage-induced birefringence of the Pockels cell. The analytical predictions are in good agreement with split-step simulations. The nonlinear polarization in the PC’s crystalline medium leads to nonlinear phase shifts and crossed-wave generation. For the small nonlinearities consistent with typical operation in a laser system, a quarter-wave PC induces a nonlinear phase equal to the average of the nonlinear phase accumulated by a linearly and circularly polarized field of the same intensity propagating in the inactive PC. The contrast of a half-wave PC between crossed polarizers is not decreased by the nonlinear propagation because there is no generated cross wave in this configuration.

Transient material properties during defect-assisted laser breakdown in deuterated potassium dihydrogen phosphate crystals

We investigate theoretically the transition from solid dielectric materials to warm solid density plasma during laser-induced breakdown in DKDP crystals (KD2PO4). Evidence taken from the experimentally measured wavelength dependence of the breakdown threshold suggests that the material excitation mechanisms mainly consist of a sequence of one-photon absorptions between short-lived vibronic defect states spanning the band gap with a quasi-continuum of states. The transition between excitation paths involving different number of photons yields information about the role of temperature in determining the width of the transition and corresponding threshold conduction band density prior to initiation of breakdown. This physical system is well adapted to study a plasma warming up at solid density leading to the so-called warm dense matter.

DKDP表面潮解对其机械性能影响的研究

本文采用显微拉曼光谱法和纳米压痕法对表面潮解后的磷酸二氘钾(DKDP)晶体进行了研究。光学显微镜下观察到样品表面出现大量微米级离散点状潮解区。拉曼光谱结果表明，潮解并未造成DKDP光谱的主要峰位发生改变。证明潮解过程并没有生成新的物质，不是化学反应。纳米压痕测试结果表明，荷载分别为10 g、20 g、30 g、40 g、50 g、60 g时，所测得的模量值和硬度值的变化趋势基本一致，在40 g模量随荷载增加从54.7 GPa下降至46 GPa (硬度从1.95 GPa下降至1.50 Gpa)，40 g以后随荷载增加模量上升至53 GPa (硬度上升至1.67 GPa)，表明DKDP表面机械性能受到潮解影响。 This deliquesced surface of DKDP, deuterated potassium dihydrogen phosphate, was studied with microscopes Raman spectroscopy and Nano-indentation. Two Raman spectra were acquired at the surface of the specimen before and after it was deliquesced. Modulus and hardness were measured with Nano-indentation under 6 different loads. Discrete deliquesced spots were observed on the surface with an optical microscope. Results show that the Raman spectra, before and after de-liquesced, are almost the same. No new products are created after deliquesced and it is not a chemical change. 6 Loads are 10 g, 20 g, 30 g, 40 g, 50 g and 60 g. The measured modulus and hardness vary with increased loads and their variation trends are nearly identical. Before 40 g, the modulus decreases with the load from 54.7 GPa to 46GPa (hardness from 1.95 GPa to 1.50 GPa). From 40 g to 60 g, the modulus raised up to 53 GPa again (hardness raised up to 1.67 GPa). Thus, the mechanical properties of the deliquesced surface have been modified.

Effect of raw material and growth method on optical properties of DKDP crystal

Three kinds of KH2PO4 raw material are used to grow deuterated potassium dihydrogen phosphate (DKDP) crystals by traditional and rapid growth methods, respectively. The growth habit dependence on the purity of raw material is described and analyzed. The optical properties including transmission spectra and laser-induced damage threshold of these crystals have been measured. It is found that the growth method affects the optical properties of crystal more obviously than the raw material with the mass content of main metal ions below 1 ppm. Moreover, the morphology of the core in the observed damage sites indicates that an explosion process probably occurs during laser-induced breakdown.